Increased activity and nuclear localisation of inositol lipid signal transduction enzymes in rat hepatoma cells

To elucidate the relationship between inositol lipid signal transduction and oncogenic transformation, the activity and subcellular distribution of phospholipase C isoforms and of phosphatidylinositol 3-kinase were analysed in Morris hepatoma cells, MH1C1, with respect to normal rat liver cells. The results provide evidence of a gain of: function of the enzymes involved in inositide signal transduction, the amount of which increased mainly at the nuclear level. Phospholipase C and phosphatidylinositol 3-kinase activities are significantly higher in rat hepatoma than in rat liver cells. Moreover, some phospholipase C isoforms are expressed at higher levels at the nuclear level; this is particularly evident in the case of the delta (1) isoform which is not expressed at the nuclear level in rat liver cells. Therefore, the autonomous nuclear signal transduction system, formerly reported as involved in the modulation of cell proliferation and differentiation, appears also affected in oncogenic transformation.